Tag: libration

Back in March 2012, I posted a remarkable video from NASA’s Goddard Space Flight Center (where I used to work) showing the motion of the Moon and how its appearance changes over the course of the year. The video went somewhat viral – probably because of the awesome music I added from Kevin Macleod – and I was pleased with it.

But then my friend, the skeptic and awesomely talented mezzo-soprano Hai-Ting Chin, asked me about libration, because she was working on a musical piece about it. She’s done several scientific songs with her partner Matthew Schickele, so it’s not as weird as it sounds. At least, not for them. Or me.

So we chatted back and forth a bit, and the result is this amazing piece of haunting and lovely music.

She sang this at the 2012 NECSS, and I wish I could’ve been there to hear it. Wow. My sister’s a mezzo-soprano, so I have some familiarity here: Hai-Ting’s voice is incredible. The piano is played by Erika Switzer.

I know the words to operatic music can be difficult to understand, so here are the lyrics:

This is animation.
Each frame represents one hour;
the whole, one year.
The moon keeps the same face to us,
but not exactly the same face.
Because of the tilt and shape of its orbit
we see the moon from slightly different angles.
In a time lapse it looks like it’s wobbling.
This is libration.
That rocking and tilting is real,
it’s called libration.

The moon’s orbit is not a circle,
but an ellipse.
The speed varies,
but the spin is constant.
Together these geometries
let us look East a little more,
then West a little more.
And the orbit’s tilt
let’s us look South a little more,
then North a little more.
This is libration.
The moon’s libration.

I love how science inspires art. Love. I hope to see more and more of this kind of scientific art as time goes on. The more ways we can show people how amazing and wonderful the Universe is, the better.

Wanna know what the Moon will look like at any time this year? And I mean what it really looks like, shadows and all?

Then go to the NASA Goddard Science Visualization Studio, where they have an amazing applet that shows you the Moon’s appearance on an hourly basis for the entire year!

Most times, websites showing you the phase of the Moon do it in big time chunks, like once per day or even per week, or they have a low-res image of the Moon with the dark part blacked out. But this one from NASA lets you enter the date and hour, for very high time resolution photo-realistic pictures.

The images are based on observations by the Lunar Reconnaissance Orbiter, which has been taken super-high-res images and altimetry data since it went into orbit our satellite in June 2009. The images show far more than just the lunar phase. For one thing, using the LRO altimeter data, it can calculate the lengths, directions, and positions of all the shadows of mountains, crater rims, and so on, knowing the angle of the Sun over the horizon.

[Make sure to set it to HD for the full effect, which is mesmerizing.]

That weird rocking and tilting motion is real. It’s called libration. The Moon’s orbit around the Earth is elliptical, so sometimes it moves faster in its orbit than other times. However, the Moon’s spin is constant. The geometry of these two things add together, allowing us to sometimes peek a little bit over the eastern and western horizons. Not only that, the Moon’s orbit is tilted a bit with respect to our Equator, so we sometimes get a little peak over the north and south poles too.

I’ll note that these views of the Moon are not designed for people at different latitudes; for example, from Australia the Moon looks upside-down compared to how I’m used to seeing it in Boulder! Instead, these views show the Moon as if you are at the center of the Earth with your head pointed toward the north pole. Still, it’s an amazing thing, and well worth bookmarking. When I need to know what phase the Moon is in — and it happens several times a month for me — this is where I’ll check.